Hi There, In this post we will learn about python errors, execptions and will learn how to handle these exceptions.

Three kinds of errors can occur in a program: syntax errors, runtime errors, and semantic errors. It is useful to distinguish between them in order to track them down more quickly.

1. Syntax errors

• Ans: Python can only execute a program if the syntax is correct; otherwise, the interpreter displays an error message. Syntax refers to the structure of a program and the rules about that structure

    >>> print "Hello world"
      File "<stdin>", line 1
        print "Hello world"
                          ^
    SyntaxError: Missing parentheses in call to 'print'. Did you mean print("Hello world")?
    >>>
  

1. Runtime errors

• Ans: The second type of error is a runtime error, so called because the error does not appear until after the program has started running. These errors are also called exceptions because they usually indicate that something exceptional (and bad) has happened.

    >>> assert 2 > 7
    Traceback (most recent call last):
      File "<stdin>", line 1, in <module>
    AssertionError
    >>>
    >>> 2 / 0
    Traceback (most recent call last):
      File "<stdin>", line 1, in <module>
    ZeroDivisionError: division by zero
    >>>
  

1. Semantic errors

• Ans: The third type of error is the semantic error. If there is a semantic error in your program, it will run successfully in the sense that the computer will not generate any error messages, but it will not do the right thing. It will do something else. Specifically, it will do what you told it to do.

These errors can be handled in python using the try except block, The exceptions that are caught in try blocks and handled in except blocks.

• syntax:

    try:
        statement 1
  		
        statement n
    except <ExceptionName>:
        statement 1
  		
        statement n
    else:
        statement 1
  		
        statement n
    finally:
        statement 1
  		
        statement n
  

• If an error is encountered, a try block code execution is stopped and transferred down to the except block.

• The except block will execute only if try block has encountered an exception that is capturing at except block.

• The else block will execute only if try block executed successfully.

• The code in the finally block will be executed regardless of whether an exception occurs.

• Example-1

    >>> try:
    ...     res = 2 / 0
    ...     print(res)
    ... except ZeroDivisionError:
    ...     print("2 can't be divided by 0")
    ... else:
    ...     print('Im else block')
    ... finally:
    ...     print('Im finally block')
    ...
    2 can't be divided by 0
    Im finally block
    >>>
  

• In the above example print statement in try block and else block were not executed due to ZeroDivisionError exception.

• finally block executed regardless of block executions

• Example-2

    >>> try:
    ...     res = 2 + 3
    ...     print(res)
    ... except Exception:
    ...     print('Im except block')
    ... else:
    ...     print('Im else block')
    ... finally:
    ...     print('Im finally block')
    ...
    5
    Im else block
    Im finally block
    >>>
  

• In the above example all blocks executed successfully except except block because there is no exception in try block execution
• Exception is the generlised excetion which can catch all python exception.

• we can also handle multiple exceptions by using defining exceptions in tuple form in except block

    except (ZeroDivisionError, AssertionError, TypeError):
        statements